(Sanitized) NOVEMBER 27, 1963 AERODYNAMICALLY HEATED WINDOW BEHAVIOR(Sanitized)

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP81B00879R001000130064-1
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 18
• Document Creation Date: December 14, 2016
• Document Release Date: December 13, 2002
• Sequence Number: 64
• Publication Date: November 27, 1963
• Content Type: REPORT

Approved For Release 2003/02/27 : CIA-RDP81 B00879R001000130064-1
November 27, 1963
.AERODYNAMICALLY HEATED WINDOW BEHAVIOR
Approved For Release 2003/02/27 : CIA-RDP81BO0879R001000130064-1
 Approved P aoRelease 2003/02/27: CIA-RDP81 B00U@R001000130064-1
1; 1
ACKNOWLEDGMENT
For c fication reasons,-this report was authored by
Most of the work contained herein, however,
was Performed on a "sterilized" basis by
STAT
00879R001.000130064-1
 Approved- Release 2003/02/27: CIA=RDP81 B0?19R001000130064-1
TABLE OF CONTENTS
SUMMARY
1. INTRODUCTION
2. SPECIFIED WINDOW DESIGN AND FLIGHT CONDITIONS
EXTERNAL FLOW CONDITIONS AND AERODYNAMIC
HEATING RATE
4. HEAT BALANCE ON THE WINDOW
5. DISUCSSION OF RESULTS
,6. SUMMARY OF LITERATURE SURVEY
REFERENCES
TABLE I
FIGURES 1 AND 2
Page
No.
Approved For Release 2003/02/27 CIA,RDP81 B00879R001000130064-1
 Approved F Zelease 2003/02/27 CIA-RDP8100 R001000130064-1
SUMMARY
This report presents the results of a 4 week study of
the behavior of an aerodynamically heated window forl ' STAT
The study revealed-that the double paned
window will retain its integrity:?and not distort sufficiently
to influence its optical quality;. The inner window surface
will operate at about 325 F and;: will radiate 446 Btu/'hr-ft2
into the instrument compartment.. Results of a literature
search on the optical and radiation . characteristics of thinly
.gold-plated glass are also included herein.
Approved Fot Release 2003/02/27 : CIA-RDP81 B00879R001000130064-1
 Approved F wRelease 2003/02/27: CIA-RDP81 B009iiR001000130064-1
AERODYNAMICALLY HEATED WINDOW BEHAVIOR
`and on November 5, 1963. This follow-on report s
.to provide a permanent record of the results of this investi-
gation.
According to the work statement of October 11, 1963,
was authorized to perform the following tasks:
a. Compute the thermal load and temperature distribution
through a specified window design for conditions
transmitted verbally to I Ion October 8,
1963.'
b. Carry out a literature survey to determine charac-
teristics of a specified gold coating and to esti-
mate its thermal effect.
_..STAT .,
The'schedule for the above activity called for preliminary
comments to be supplied by November 4, 1963 and a final report
by November 11, 1963. A report of the final; results was
delivered verbally by the author to 'STAT
to be mounted flush with the outer skin of the'aircraft. in
the absence of any information regarding the thermal boundary
condition on the inner portion of the skin, no consideration
has been made of the possible effects caused by the window
outer surface being at a different temperature than the up-
stream skin.
window composed of two panes separated by'a gap. The outer
pane is made of Quartz (Si02) and the inner pane of Schott
BK-7. Both panes are 0.400-inch thick and are taken to be
?11.53 inches along the axis of the aircraft and 17.97 inches
in the span direction. A gap thickness of 0.08 inch was con-
sidered as the nominal gap dimension. The window was assumed
SPECIFIED WINDOW DESIGN AND FLIGHT CONDITIONS
The window design considered in the current study is a
The thermal behavior of the window was studied for the
case where the window is mounted on the lower surface of an
aircraft flying at, a Mach number of 3.2 at an altitude of
85,000 feet. The leading edge of the window was located at
station.720 of the aircraft. The aircraft bottom was assumed
to behave as a flat plate at an angle of attack.of 70.
Approved For Release 2003/02/27 CIA-RDP81800879R0'01000130064-
 Approved P%&Release 2003/02/27: CIA-RDP81 B00 R001000130064-1
-2-
EXTERNAL FLOW CONDITIONS AND AERODYNAMIC HEATING RATE
At an altitude of 85,000 feet the local atmospheric
conditions are as follows:
edge of the boundary layer over the window to be as follows:
temperature, Too -.3940 R
pressure, p. - 4.6 lb/ft2 = 0.0218 atm
velocity of sound, a.0 - 972 ft/sec
density, p0 6.8x10 5 lb sect / (ft) 4,
velocity, u, = 3.11x103 ft/sec
The compression that takes place in the shock wave ahead of the
plate at 7? angle of attack alters these conditions at the
temperature, Ts = 4670 R
pressure, p0 =0.0372 atm
velocity, ub ? 2.975x103 ft/sec
For these local conditions, the convective heat flux to the
window can be expressed as
Ts.
cp (Tr_T6)
convective heating, coefficient
38.5
T1 0.84;
Ta
(1)
(2)
specific heat of air0.24 Btu/lb OR
recovery temperature
u
+ r 2g 6 cp 467 + 667 = 1134? R (3)
outer window temperature
T1 reference temperature at which to evaluate
properties
Approved For R am 2?034211 70 -2[ 816081T.941130064-1 (4)
0
 Approved F e wRelease 2003/02/27: CIA-RDP81 B00$idR001000130064-1
-3-
of the heat balance equations for the window. ,
solution
'in the temperature potential term does not have to be pre
scribed initially in that it is obtained explicitly in the
usually needed in this iteration process. Note that T
The manner of solution was to assume a reasonable value of
T in Equation (4), solve for the surface temperature, and
s
to iterate until convergence occurred. Only two steps were
From Equations (2) and (4), it can be observed that CH is
dependent on T and therefore Equation (1) is nonlinear.
6
The heat balance performed on the window is indicated
schematically in Figure 1. The assumptions employed in this
heat balance are as follows:
Steady-state, the windows are exposed sufficiently
long to be at equilibrium.
All heat flow is unidirectional.
c. The air in the gap between the windows is stagnant..
d. Convection patterns over the inner surface of the
window are uniform.1 i
The symbols employed in the heat balance are indicated in
Figure 1 and are defined generally as follows:
T
Ts
temperature, OR
emissivity expressed as a function of the
glass temperatures
Stefan-Boltzmann constant
thermal conductivity of the glasses as a
function of,average temperature of. the
windows
width of window or gap
convective heat-transfer coefficient on
the inside of the window introduced by
free convection or internal blowing
internal cooling air temperature
internal mean surface temperatures
Approved For Release 2003/02/27 CIA-RDP81B00879R001000130064-1
 Approved Fe lease 2003/02/27: CIA-RDP81 B00>lip001000130064-1
Id,
-4-
unknown temperatures T , T , T , and T .
A balance on the heat flux in and out of each surface yields
four simultaneous equations that can be solved for the four
6 7 9 10
DISCUSSION OF RESULTS
For all the computations presented here, it was assumed
that the internal air passing over the window and the interior'
surfaces were maintained at 70? F or 530? R.
The first effect studied was that introduced by varying
the internal convective heat-transfer coefficient. It was
estimated that the expected elevated window temperature and
its nearly horizontal position at the bottom of the cavity
would cause free convection and an internal heat-transfer
coefficient of about 0.25 Btu/hr-ft2 ?F. Because this value
could be dimished by configuration effects if the window is
recessed, it was decided to run calculations for an internal
heat-transfer coefficient ranging from half the expected free
convection coefficient to ten times this value. The increased
heat-transfer coefficient can be caused by air circulation
fans.For the nominal internal free-convection conditions,
,the:following results were obtained
radiation heat fluxtoinstrument 446'Btu/hr-ft2
total heat flux to.instrument 509 Btu/hr-ft2
outer window,
outer window,
inner window,
inner window,
These temperatures are well.within the useful ranges of the
glasses considered.
The effect of varying the internal heat-transfer coeffi-
cient is shown in Figure 2. In this figure the inner window.
inside temperature, and the heat load, to the instrument com-
partment are shown as functions of the inside heat-transfer
coefficient. This figure indicates that a ten-fold increase
of the internal convection coefficient can cause a sizeable
reduction in the internal surface temperature, approximately
800 F, but this also increases the amount of heat transferred.
to the camera compartment by about 40 percent. The 800 F
change in temperature reduces the radiant heat flux from the
window by 41 percent. The largest increase shown in the
internal convective coefficient only causes about a 250 F
reduction in the external window temperature; therefore,
increasing the internal convective coefficient will not alter
,the strength of the window significantly. The main advantage
of lowering the inner window temperature is the reduction of
heat flux radiated from the window to the lens rather than
strt g .Fo le 3MEU }S~~v 1 $ 1Q j.~30A flux
and increasing.the air. turbulence in the light path from an
exterior
temperature
4460 F
gap-side
temperature
4289 F
gap-side
temperature
3490 F
inside temperature
325? F
 Approved F oOelease 2003/02/27 : CIA-RDP81600 001000130064-1
.t
optical viewpoint, however, will require careful study in the
development of the current system.
Another means was considered for reducing the window
inner temperature. This consisted of applying an optically
semi-transparent film of gold on one of the four window sur-
faces. The gold film characteristics used in this study
were obtained in a literature survey that is described in
.the next section of this report. A conservative figure of
0.08 was used for the gold film emissivity and the results
of this study are shown in Table I. The nominal condition in
the absence of any gold is also shown for reference. The
following observations can be deduced from the table:
a. Placing the gold on the exterior surface of the
window, 6 of Table I, causes a rise in temperature
of both panes. The reason for this is the reduction
of the heat rejected by radiation to space by the
window because of the low emissivity of the gold.
Under this condition both the radiated and total
heat load into the camera compartment are increased.
Placing the gold on either of the inner gap surfaces,
7 or 9 of Table I, produces an identical effect.
It increases the outer window temperature slightly
above the nominal case, and reduces the inner win-
dow temperature. The radiation from the inner win-
dow is reduced about 16 percent and the total heat
.load is also reduced.
Placing the gold on the interior surface, 10 of
Table I, blocks the heat from entering the camera
cavity and consequently causes both window tempera-
tures to rise. The rise in temperature of the inner
surface, however, does not compensate for the reduc-
tion of the emissivity of the gold, and the heat
flux radiated toward the lens is only 18 percent of
the nominal case. Another, advantage of this case
is the reduction of the temperature gradients within
the glass plates and,. consequently, reduced bending.
Deflection calculations were performed under the assump-
tion of unrestrained edges. The; deflections at a radius of
6 inches from the center of the window, for the nominal temper-
ature conditions, were 108 ? and 226 ? in.the outer and inner
windows, respectively (? - 0.56,).
A literature survey was conducted on the subjects of the
transmittance, absorptivity, and reflectivity of metallic
goWpdiv]dd:omiRe sa003/ I4l7r ?BQ76MO -1Jniversity
 Approved Fbo Release 2003/02/27 : CIA-RDP81 B00WR001000130064-1
Library, and the library at Lockheed
Missiles and Space Company, Sunnyvale, provided the basic
sources of open available technical information related to
the transmittance, absorptivity, and reflectivity of metallic
gold films on glass.
References 1 to 6 list the major journals reviewed in
this survey; the results of which are rather unproductive.-
.References 7 to 13 were found in these journals which are
,related to the subject area but all failed to provide infor-
mation applicable to this specific subject.
The Armed Services Technical Information Agency (ASTIA)
performed a literature search, in conjunction with our request,
on this subject area. The results of this search listed
approximately 300 references, all of which related in some
way to the subject area but none appeared to'be applicable
.to our specific problem except.those already obtained from'
the other mentioned sources.
References 14 to 22 are related reports presently avail-
able in However, none of these except
Turner's paper (Ref. STAT.
specifically discusses metallic gold films.
The most comprehensive source on the subject is Heavens'
book "Optical Properties of Thin Solid Films" (Ref. 23). It
appears that this book presents the most complete analysis
of the technological aspects of thin film optics available.
The most pert'inent paper; however, remains Turner's
paper (Ref. 22). Unfortunately, the application of Turner's
data raises almost as many questions as it answers. The
major disadvantage to Turner's paper for the present problem
is due to the wavelength region currently considered. Other
.factors, such as the rate of disposition, method of appli-
cation, and complete definition of curves, tends to add con-
fusion.
In spite of various problems, Heaven's book and Turner's
paper (Refs. 23 and 22) were the best references found in
the process of this literature search.
The one company that has apparently issued the greatest
number of reports in the subject area is the Bausch and Lomb
.Optical Company of Rochester, New York. Published reports
indicate that this company has been actively engaged in
experimental and theoretical research in this area at least
,,for the past 15 years. The next step in this literature
search should definitely be centered toward communications
with this company.
Approved For Release 2003/02/27 CIA-RDP81 B00879R001000130064-1
 Approved Release 2003/02/27: CIA-RDP81 B008001000130064-1
-7-
The following references are presented as references
pertaining to the general area, but very few deal with the
;specifics. desired.
Approved For Release 2003/02/27 CIA-RDP81 B0.0879R001000130064-1
 Approved F elease 2003/02/27 : CIA-RDP81 B001 l 001000130064-1
REFERENCES
1. Journal of the Society of Glass, Society of Glass
Technology. Thornton Publishing Co., Sheffield, England,
1935 to 1959.
2. Physical Society Proceedings, Institute of Physics and the
Physical Society. London, England, 1935 to present.
Journal of American Ceramic Society. Columbus, Ohio,
1935 to present.
. Journal of Optical Society of America, American Institute
of Physics. New York, N. Y., 1935 to present.
. Applied Science and Technology Index. H.W. Wilson
Company, New York, 1940 to present.
6. Journal of Metals, American Institute of.'Minning and
Metallurgical Engineers. 1940 to 1962.
7. Gillham, E. J. and Preston, J. S.: Transparent Conducting
Films. Physical Society Proceedings B, 1952, 65(8).
8. Greenland, K. M.: Interference Filters. Endeavour.
July 1952, 11, 143-148.
9. Anderson., S. and Kempton, D. D.: Interference Films on
Glass. Journal of American'Ceramic Society, 1953,
36(6) 175-179.
10. Giffken, W.: Thin Films on Glass (In German) Glastick,
Ber., 1951, 24(6). Schott Company.
11., Greenland, K. M.: The Measurement and Control of the
Thickness of Thin Films. Vacuum. 1952, 2(3), 216-230.
12. Kerridge, F. E.: Metallic Films. Presented at the 159th
Meeting, London Section of the Society of Glass Technology,
March 2, 1954.
13. Strong, J.: Practical Applications of High and Low
Reflector Films on Glass. Glastick, Berlin, 1953, 26(4),
124.
14. Olsen, A. L., Nichols, L. W., and Regelson, E.: Trans-
mittance of Infrared Energy. NAVORD Report 5584, China
Lake, California, October 9, 1957.
15. Eberly, D. K.: Radiative Properties of SiO Coatings on
Vacuum Deposited Aluminum Films. STAT
August 19, 1960.
Approved For Release 2003/02/27 : CIA-RDP81 B00879R001000130064-1
 Approved F2elease 2003/02/27 : CIA-RDP81 B00>001000130064-1
16. The Structure of Glass, Vol. I (Translated from Russian).
Proceedings of a Conference
on the
Structure
of Glass,
Leningrad, November 23-27,
New York, 1958.
1953.
Consultants
Bureau,
17. The Structure of Glass, Vol. II (Translated from Russian).
Proceedings of the Third All-Union Conference on the
Glassy State. Leningrad, November 16-20, 1954.
Consultants Bureau, New York, 1960.
`18.:Shaw, C., Berry, J., and Lee, T.: Spectral and Total
Emissivity Apparatus and Measurements of Opaque Solids.
'LSMD No. 48488, Lockheed Aircraft Corporation, Sunnyvale,
California, March 1959.
19. Surface Effects on Spacecraft Materials., First Symposium
held at Palo Alto, California, May 12 and 13, 1959.
Sponsored by Air Research and Development Command, U. S.
Air Force and Missiles and Space Division, Lockheed
Aircraft Corporation. Edited by Francis J. Clauss.
John Wiley and Sons, Inc., 1960.
20. Materials Handbook. Corning Glass Works, Corning, New
York.
21. 'Optical Glass, Tables of Characteristics. JENAer Glaswerk
Schott and Gen., Mainz, Western Germany.
22. Turner, A. F.: An Interference Type Heat Reflecting
Filter. Bausch and Lomb Optical Co., Journal of Optical
Society American, 37, 982(A), 1947. Presented at
Cincinnati Meeting, October 23 - 25, 1947, optical
Society of America -
23. Heavens, 0. S.: Optical Properties of Thin Solid Films.
Academic Press Inc., New York, 1955.
24.Holland, L.: Vacuum Deposition of Thin Films. John
Wiley and Sons, Inc., New York, 1956.
25. Harris, E. J.: Some Measurements of Infrared Transmission
of Glass and Plastics. (Telecommunications Research
Establishment (Gt. Britain) 1950 (5)p. incl. illus.
_(Rept. No. L3/25, Encl.. No,. 5 to Naval Attache, London,
Ser. No. 270; CRB Ref. No. 46/2412). AD-147 688
STAT
.26. Glaze, F. W.., Osmalov, J. H., and Capps, W.: Development STAT
of Glasses for Transmitting Infrared Energy. Quarterly
'Report No. 1 for period ending 15 December 1953, 10 p.
Approved For Release 2003/02/27: CIA-RDP81 B00879R001000130064_1.
 Approved F elease 2003/02/27 : CIA-RDP81 B00 W001000130064-1
STAT
27._ Glaze, F. W., and Capps, W.: Development of Glasses for
(NBS Report No. 3173),
STAT
Turner, A. F.: Infrared Transmission Filters. Bausch .STAT
Transmitting Infrared Energy. National Bureau of
Standards, Washington, D. C. Quarterly Report No. 2
for period ending 15 March 1954, 10 p. illus. tables
1953, IV Incl., illus. tables,
and Lamb Optical Co., Rochester, N. Y. Quarterly
Technical Report No. 3, 23 October 1952 - 22 January
0
290' Bartle, L., and Mooney, a' Infrared Transmission Filters.
Bausch and Lomb Optical Co., Rochester, N. Y. Quarterly
Technical Report No. 4, 23 January - 22 Aril 1953
20 P. incl. illus. table, STAT
30. Bartle., L. and Mooney, F.: Infrared Transmission Filters.
illus . F
I STAT
Technical Report No. 5, 23 April - 22 July 1953, 9 p.
-
Bausch and Lomb Optical Co., Rochester, N. Y. Quarterly
31. Bartle, L., Mooney, C. F., and Turner, A. F.: Infrared
Transmission Filters. Bausch and Lomb Optical Co.,
Rochester, N. Y. Quarterly Technical Report No. 6,
23 July - 23 October 1953,`34 p. illus.
STAT
32. Turner, F. A.: Infrared Transmission Filters. Bausch
34. Kreidl, J. J.: Investigation of Infrared Transmitting
Materials. Bausch and Lomb Optical Co., Rochester, N. Y.
Quarterly'Report No. 1, 1 January - 1 April 1955, 24 p..,
and Lomb Optical Co., Rochester, N. Y. Quarterly
Technical Report No. 7, 23 October 1953 - 22 January
1954, 9 p. illus. STAT
a
Bartle, L. and Mooney, F.: Infrared Transmission Filters.
Bausch and Lomb Optical Co., Rochester, N. Y. Quarterly
Technical Report No. 8, 23 January - 23 May 1954, 9 p.
illus . STAT
incl. illus. tables. STAT
35. Kreidl, J. J.: Investigation of Infrared Transmitting
Materials. Bausch and Lomb Optical Co., Rochester,, N.Y.
Progress Report No. 3, 1 July - 1 September 1955, 41 p.
incl. illus. tables. STAT
Approved For Release 2003/02/27 : CIA-RDP81800879R001000130064-1
 Approved F-Release 2003/02/27: CIA-RDP81 B00MOR001000130064-1
36. Kreidl, J. J., Hafner, H. C., and others: Investigation
of Infrared Transmitting Materials. Bausch and Lomb
Optical Co., Rochester, N. Y. Report for January 1955 -
January 1956 on Ceramic and Cormet Materials. July 1957
150 P. incl. illus. tabl
STAT
37. Kreidl, J. J.: Investigation of Infrared Transmitting
Materials. Bausch and Lomb Optical Co., Rochester, N. Y.'
Report No. 1 1 April - 1 July 1957, 90 P. incl. illus.
tables. STAT
tables.
Report No. 2 1 November 1957, 54 incl. illus.
.38. Kreidl,. J. J.: Investigation of Infrared'Transmitting
Materials. Buasch and Lomb Optical Co., Rochester, N. Y.
October 1958, 266 p. incl. illus. tables.
Optical Co., Rochester, N. Y. Report for January 1956 -
January 1957 on Ceramic and Cormet Materials.
39. Kreidl, J. J., Hafner, H. C., and others: An Investigation
of Infrared Transmitting Materials. Bausch and Lomb STAT
40. ?Kreidl, J. J., Hafner, H. C., and others: Investigation
of Infrared Transmitting Materials. Bausch and Lomb
Co., Rochester, N. Y. Report for January 1957 -. January
1958 on Ceramic and Cormet Materials Pt. 3 October
STAT
Approved For Release 2003/02/27 : CIA-RDP81 B00879R001000130064-1
 Approved F2elease 2003/02/27: CIA-RDP81 B00>M'R001000130064-1
TABLE I.- EFFECT OF GOLD FILM ON
61
6
7
9
10
gold foil ?F OF ?F OF Btu/hr-ft Btu/hr- ft2
none
ONE OF THE WINDOW SURFACES.
9 10
~, ; / interior
T6 T7 T9 T10 Qrad Qload
445.6
427.9
348.9
32
4.6
446
539.7
516.0
420.6
38
7.5
636
452.9
437.8
319.0
29
8.0
377
452.9
437.8
319.0
29
8.0
377
477.4
471.5
448.3
44
0.4.
79
Approved For Release 2003/02/27 : CIA-RDP81 B00879R001000130064-1
 Approved For Release 2003/02/27 : CIA-RDP81 B00879R001000130064-1
Figure 1.- Schematic diagram of heat balance employed on window.
Approved For Release 2003/02/27 : CIA=RDP81 B00879R001000130064-1
 Approved For Release 2003/02/27 : CIA-RDP81 B00879R001000130064-1
internal gas temperature = 5300 R
700L
0
I
1.0
1
2.0
I I
internal convective heat-transfer coefficient, Btu/ft2, hr, of
Figure 2.Effect of internal convective heat-transfer coefficient on inside
temperature and heat load.
Approved For Release 2003/02/27 CIA-RDP81 B00879R001000130064-
L 800